Wettability assessment of fracturing proppants for improving fluid recovery

ABSTRACT

Methods, systems, and apparatus for analytical wettability assessment of fracturing proppants for improving fluid recovery are disclosed. Embodiments include determining, for a proppant sample, a first value related to an oil-wet index of the proppant sample. Embodiments further include determining, for the proppant sample, a second value related to a water-wet index of the proppant sample. Embodiments further include determining, for the proppant sample based on the first value and the second value, a third value related to a wettability index of the proppant sample. Embodiments further include determining, based on the third value, a wetting characteristic of the proppant sample. Other embodiments may be described.

TECHNICAL FIELD

This description relates generally to fracturing proppants, for example,to analytical wettability assessment of fracturing proppants forimproving fluid recovery.

BACKGROUND

Hydraulic fracturing proppants are typically solid materials, such assand or ceramics designed to keep an induced hydraulic fracture open forfracturing. A proppant can be added to a fracturing fluid that can varyin composition. Trade-offs are sometimes made in the material propertiesof fracturing fluids, such as viscosity, where more viscous fluids canimprove a proppant's carrying capacity. The pressure needed for aparticular flow that conducts the proppant can also be traded-off withother factors. However, traditional methods to measure wettability ofproppants are typically rudimentary, for example, examination using thenaked eye or judging a droplet's shape; or indirect such as using thecapillary rise method. Therefore, the wettability performance ofproppant samples within a wettability category can often not be comparedaccurately.

SUMMARY

Methods, systems, and apparatus for analytical wettability assessment offracturing proppants for improving fluid recovery are disclosed. Awettability measurement system removes moisture from at least one fluidline of the wettability measurement system using a solvent. Thewettability measurement system injects a proppant sample into a vesselof the wettability measurement system. The vessel has a diameter lessthan a dimension of a wettability measurement instrument of thewettability measurement system. A flat surface of the wettabilitymeasurement system applies pressure on a proppant surface of theproppant sample, such that the proppant surface is level. Thewettability measurement system places the vessel into the wettabilitymeasurement instrument, such that the vessel is centered with respect toa dropping needle of the wettability measurement system. The droppingneedle of the wettability measurement system applies a droplet ofdeionized water or a hydrocarbon onto the proppant surface. Thewettability measurement system captures an image of the dropletcontacting the proppant sample to provide a wettability assessment ofthe proppant sample.

In some implementations, the wettability measurement system determines acontact angle of the droplet and the proppant sample based on the image.The wettability assessment is based on the contact angle.

In some implementations, moisture is removed from the proppant sampleusing an oven.

In some implementations, the proppant sample is positioned inside thewettability measurement instrument, such that a distance between thedropping needle and the proppant sample is in a range of distances.

In some implementations, the proppant sample is positioned inside thewettability measurement instrument, such that the droplet contacts theproppant sample at a location greater than a threshold distance from awall of the vessel.

In some implementations, the image of the droplet contacting theproppant sample is captured within a threshold time after the droplet isapplied onto the proppant surface.

In some implementations, the vessel is positioned inside the wettabilitymeasurement instrument, such that the vessel is level.

In another embodiment, methods, systems, and apparatuses are disclosedfor determining, for a proppant sample, a first value related to anoil-wet index of the proppant sample; determining, for the proppantsample, a second value related to a water-wet index of the proppantsample; determining, for the proppant sample based on the first valueand the second value, a third value related to a wettability index ofthe proppant sample; and determining, based on the third value, awetting characteristic of the proppant sample.

In some implementations, the first value related to the oil-wet index ofthe proppant sample is based on a contact angle of the proppant withrespect to oil.

In some implementations the second value related to the water-wet indexof the proppant sample is based on a contact angle of the proppant withrespect to water.

Some implementations further include determining, based on the firstvalue and the second value, a fourth value related to a neutralityindex; and validating, based on the fourth value, a neutrality of theproppant sample.

In some implementations, the first value relates to an affinity of theproppant sample for oil.

In some implementations, the second value relates to an affinity of theproppant sample for water.

In other embodiments, systems, methods, and apparatus for athree-dimensional (3D)-printed vessel for wettability assessment offracturing proppants are disclosed. The vessel includes a base componentincluding a threaded cylindrical portion extending outward from a firstside of the base component. The cylindrical portion has a particularthread profile. The base component defines a cavity sized to contain aproppant sample. A cap is configured to be screwed onto the threadedcylindrical portion after the proppant sample is injected into thecavity. A surface of the cap is shaped to flatten a proppant surface ofthe proppant sample. The cap is threaded with the particular threadprofile. A pin is configured to be partially screwed onto a second sideof the base component before the proppant sample is injected into thecavity. The second side is opposite to the first side.

In some implementations, the vessel is printed using at least one ofengineering plastic, tough resin, or acrylonitrile butadiene styrene(ABS).

In some implementations, the cap is further configured to apply pressureto the proppant surface when the cap is screwed onto the threadedcylindrical portion, such that the proppant surface is level.

In some implementations, a diameter of the vessel is in a range from 2.5cm to 3 cm.

In some implementations, a length of the vessel is in a range from 3 cmto 4 cm.

In some implementations, the pin has a hexagonal opening sized toreceive a screwdriver to screw the pin onto the second side of the basecomponent.

In some implementations, the pin is further configured to be fullyscrewed onto the second side of the base component after the proppantsample is injected into the base component.

In some implementations, the cap is further configured to be tightenedby a wrench after the cap is screwed onto the threaded cylindricalportion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates example contact angle values of proppant sample usingdifferent fluids, measured at 25° C., in accordance with one or moreimplementations.

FIG. 2A illustrates example contact angle measurement using deionizedwater, in accordance with one or more implementations.

FIG. 2B illustrates example contact angle measurement using acondensate, in accordance with one or more implementations.

FIG. 3 illustrates an example wettability index, in accordance with oneor more implementations.

FIG. 4 illustrates example results of wettability parameters, inaccordance with one or more implementations.

FIG. 5 illustrates an example visualization of a computed wettabilityindex of different hydrocarbons, in accordance with one or moreimplementations.

FIG. 6 illustrates an example cap of a three-dimensional (3D)-printedvessel for wettability assessment of fracturing proppants, in accordancewith one or more implementations.

FIG. 7 illustrates an example cap of a 3D-printed vessel for wettabilityassessment of fracturing proppants, in accordance with one or moreimplementations.

FIG. 8 illustrates an example base component of a 3D-printed vessel forwettability assessment of fracturing proppants, in accordance with oneor more implementations.

FIG. 9 illustrates an example pin of a 3D-printed vessel for wettabilityassessment of fracturing proppants, in accordance with one or moreimplementations, in accordance with one or more implementations.

FIG. 10 illustrates an example pin of a 3D-printed vessel forwettability assessment of fracturing proppants, in accordance with oneor more implementations.

FIG. 11 illustrates example components of a 3D-printed vessel forwettability assessment of fracturing proppants, in accordance with oneor more implementations.

FIG. 12 illustrates an example assembly of a 3D-printed vessel forwettability assessment of fracturing proppants, in accordance with oneor more implementations.

FIG. 13 illustrates an example computer system for wettabilityassessment of fracturing proppants, in accordance with one or moreimplementations.

FIG. 14 illustrates an example process for using a 3D-printed vessel forwettability assessment of fracturing proppants, in accordance with oneor more implementations.

FIG. 15 illustrates an example process for wettability assessment offracturing proppants, in accordance with one or more implementations.

FIG. 16 illustrates an example process for identifying a wettabilityindex of fracturing proppants, in accordance with some implementations.

DETAILED DESCRIPTION

The implementations disclosed provide systems and apparatus for athree-dimensional (3D)-printed vessel for wettability assessment offracturing proppants. Wettability refers to an ability of a liquid tomaintain contact with a solid surface. This phenomenon results from theintermolecular interactions between the solid and fluid phases.Wettability can be measured using contact angle analysis. However, forsmall spherical or irregular particles, direct wettability measurementposes challenges when using traditional methods. Using theimplementations disclosed herein, wettability assessment of sphericalobjects is performed to enable numerical wettability measurements ofsmall spherical surfaces (for example, having a mesh size of 5-80) usinga pendent drop method. In some implementations, a drop shape analyzer(DSA) is used.

Among other benefits and advantages, the implementations provide aflexible and integrated system and apparatus for a 3D-printed vessel forwettability assessment of fracturing proppants. The implementationsprovide direct and precise wettability assessments for fracturingproppants. The direct measurement approach provided by the 3D-printedvessel enables improved classification and comparison of wettabilityperformance for proppant samples having similar wettability features.The measurement success rate improves and measuring time decreases. Inaddition to improvements in preparing spherical samples for contactangle measurement, the advantages provided by the 3D-printed vesselinclude a reduced leveling time (proppant preparation), increasedefficiency by increasing the success rate, improved ability to preventthe droplet from sinking and falling between proppant particles for alonger period of time, an eliminated wall effect, and improved levelingand maintenance of proppant surfaces. In fact, the implementationsdisclosed herein are not limited to wettability assessment of proppantsand can be applied to wettability assessments of many small irregularlyshaped particles.

FIG. 1 illustrates example contact angle values of proppant samplesusing different fluids, measured at 25° C., in accordance with one ormore implementations. The implementations disclosed herein addresswettability assessment of small spherical objects, generally. Theimplementations thus enable and facilitate numerical wettabilitymeasurement of small spherical surfaces (for example, having a mesh sizeof 5-80) using a pendant drop method based on the KRUSS drop shapeanalysis (DSA)-100. Wettability refers to an ability of a liquid tomaintain contact with a solid surface. Wettability results from theintermolecular interactions between the solid and fluid phases. Apendant drop refers to a droplet suspended from a needle in a bulkliquid or gaseous phase. Wettability is assessed by measuring a contactangle between the droplet and the bulk fluid, sometimes called a directmeasuring approach. The wettability assessment can include computing theindices illustrated and described in more detail with reference to FIG.5 .

In some implementations, a wettability measurement system injects aproppant sample into a vessel 1200 of the wettability measurementsystem. The wettability measurement system can include a wettabilitymeasurement instrument, such as the KRUSS DSA-100, an actuator (such asimplemented in a robotic arm) to perform physical actions on the vessel1200 and the wettability measurement instrument, and a computer system1302 to control the wettability measurement instrument and the actuator.The vessel 1200 is further illustrated and described with reference toFIG. 12 . The computer system 1302 is further illustrated and describedwith reference to FIG. 13 . The wettability measurement system applies,by a dropping needle, a droplet of deionized water or a hydrocarbon ontothe proppant surface. The computer system 1302 captures an image of thedroplet contacting the proppant sample to provide a wettabilityassessment of the proppant sample. The computer system 1302 determines acontact angle of the droplet and the proppant sample based on the image,such that the wettability assessment is based on the contact angle.

Example experiments were conducted to measure the obtained contact angleof proppant samples with deionized water and other hydrocarbon fluidphases. Example results obtained for contact angle measurements and thespecific gravity of fluids at T=25° C. are shown in FIG. 1 . In FIG. 1 ,the hydrocarbons labeled “condensate” represent condensate sampleshaving different compositions.

FIG. 2A illustrates example contact angle measurement using deionizedwater, in accordance with one or more implementations. Exampleexperiments were conducted on high-strength ceramic proppants. Thewettability was altered to neutral characteristics by coating thesamples. In some implementations, prior to measuring the contact angle,the wettability measurement system removes moisture from at least onefluid line of the wettability measurement system using a solvent. Thewettability assessment system is illustrated and described in moredetail with reference to FIGS. 1, 11, and 13 . To prepare the system forcontact angle measurement, the wettability measurement system iscalibrated. The fluid lines are cleaned and dried. For example, solventsare used to ensure the absence of fluids inside the lines. This step isperformed to prevent fluid remains (for example, leftover fluids fromprevious measurements) that can mix with the testing phase, and alterits properties and affect the wettability results.

In some implementations, the wettability measurement system removesmoisture from the proppant sample using an oven. For example, theproppant samples can be heat aged at a temperature in a range betweenapproximately 50 degrees Celsius (° C.) and approximately 80° C. toensure moisture removal. It will be understood that this temperaturerange is intended as an example temperature range, and other temperatureranges may be used in other embodiments based on factors such as thetype of proppant, etc.

The proppant samples tested in the experiments with reference to FIG. 2Aare high-strength ceramics. The wettability measurement system injects aproppant sample into a vessel 1200 of the wettability measurementsystem. The vessel 1200 is further illustrated and described withreference to FIG. 12 . In some implementations, the vessel 1200 has adiameter less than a dimension of the wettability measurementinstrument, described in more detail with reference to FIG. 1 . Forexample, the proppant sample is injected into a transparentsemi-cylindrical vessel having an outer diameter that is less than aninner dimension of the wettability measurement instrument.

In some implementations a flat surface of the wettability measurementsystem is used to apply pressure on a proppant surface of the proppantsample, such that the proppant surface is leveled. For example, thevessel 1200 is filled with the proppant sample and a pressure is appliedto the surface of the proppant sample by a flat surface. The flatsurface can be a surface of the cap 600, illustrated and described inmore detail with reference to FIG. 6 . The application of the pressureis repeated until the proppant surface is optimally leveled. Theproppant surface is leveled to reduce the effect of spaces betweenproppant particles.

In some implementations, the wettability measurement system places theproppant sample in the vessel 1200 into the wettability measurementinstrument, such that the vessel 1200 is centered with respect to adropping needle of the wettability measurement system. For example, theleveled proppant sample in the vessel 1200 is placed gently inside thecontact angle measuring cell. The vessel 1200 is positioned inside thewettability measurement instrument, such that the vessel 1200 is level.The vessel 1200 is centered below the dropping needle and positioned atthe zero horizontal level (that is, not tilted). Instrumentally,leveling the proppant surface by the disclosed implementations, as wellas maintaining the leveling of the proppant surface throughout themeasurement process, is key to the success of the measurement.

In some implementations, the proppant sample is positioned inside thewettability measurement instrument, such that the droplet contacts theproppant sample at a location greater than a threshold distance from awall of the vessel 1200. Thus, wall effect is reduced or eliminated. Thedroplet is prevented from touching or approaching the walls of thevessel 1200 using the disclosed implementations. When traditionalmethods are used, touching or being close to a vessel wall can cause thedroplet's adhesion to be dominated by the wettability of the vesselitself and not the proppant sample. For example, when water is appliedto a graduated cylinder, the fluid surface will be curved creating ameniscus caused by the fluid's attachment to the walls. Using theimplementations disclosed herein, the proppant sample is positionedaccurately below the dropping needle instead to mitigate wall effect. Insome implementations, the size of the vessel 1200 is increased, furtherdecreasing the wall effect, for example, in case a wall effect isobserved.

In some implementations, the proppant sample is positioned inside thewettability measurement instrument, such that a distance between thedropping needle and the proppant sample is in a range of distances. Thedropping needle is thus positioned at a vertical position that is nottoo far away from the proppant surface nor too close to the proppantsurface. A higher vertical position of the dropping needle (greaterdistance between the dropping needle and the proppant sample) can resultin a greater gravitational acceleration force of the falling droplet andcause a scattering of proppant particles upon landing. On the otherhand, positioning the dropping needle too close to the proppant surfacecan cause attachment of a few proppant particles to the droplet beforethe droplet is completely detached from the dropping needle.

In some implementations, the image of the droplet contacting theproppant sample is captured within a threshold time after the droplet isapplied onto the proppant surface. For example, after the droplet isreleased, the image is frozen within a threshold time in a range ofseven to twelve seconds. The threshold time is designed to mitigate theeffects of pore spaces between proppant particles. In someimplementations, the wettability measurement system (for example, thecomputer system 1302) determines the contact angle of the droplet andthe proppant sample based on the image. The computer system 1302 isfurther illustrated and described with reference to FIG. 13 . Thewettability assessment is based on the contact angle. For example, thecontact angle of the proppant sample with the droplet phase is computedusing software on the computer system 1302. The wettability assessmentcan include computing the indices illustrated and described in moredetail with reference to FIG. 5 . Because of a combination ofunavoidable spaces between proppant particles and gravitational forces,the droplet can sink between proppant particles. Hence, theimplementations disclosed herein are used to conduct measurements in atimely fashion; the image of the contact angle is frozen within thethreshold time after the droplet is applied. The implementationsdescribed herein were used to measure the contact angles of proppantsamples with deionized water (FIG. 2A).

FIG. 2B illustrates example contact angle measurement using acondensate, in accordance with one or more implementations. Theimplementations described herein were used to measure the contact anglesof proppant samples with different hydrocarbon fluid phases. The averagecontact angle measured with deionized water phase was 118.5° compared toa range of 84.5°-113.9° for hydrocarbons, depending on the type. Forheavier hydrocarbon components (Hexane and Octane), the dropletsflattened out immediately after being dropped, making the measuring ofthe contact angle more challenging. This indicates that heaviercomponents have a better affinity to the proppant sample, and thus lowervalues of contact angle (less than 30°).

FIG. 3 illustrates an example wettability index, in accordance with oneor more implementations. The contact angle value for a single phase byitself typically offers less insight into the wettability aspect of aproppant sample, given that wettability refers to the tendency of afluid to adhere to a surface in the presence of another immisciblefluid. In some implementations, therefore, interpretations of contactangle measurement of one phase (water or oil) are performed in relationto the other phase. For example, two oil and water fluid phases can berelated to evaluate an overall wettability for proppant samples. Thefollowing equations can be used correlate the contact angle of oil andwater phases, and determine a single wettability value to represent thewettability status of proppant samples.OWI=(180−θ_(oil)/180  (1)Here OWI denotes an oil-wet index and θ_(oil) denotes the contact anglewith respect to oil. Next,WWI=(180−θ_(water))/180  (2)

Here, WWI denotes a water-wet index and θ_(water) denotes a contactangle with respect to water. Equations (1) and (2) can be used todetermine a deviation of the contact angle from neutrality for eachfluid phase. The values for OWI and WWI are in the range of (0, 1),where zero (0) signifies a complete wetting characteristic and one (1)characterizes a strong adherence of the phase. Similarly,WI=WWI−OWI  (3)

The wettability index “WI” combines the water and oil wettabilityindices into a single index. The WI index values range from −1, whichcharacterizes a strong oil wettability character to 1, indicating astrong water wettability character. Finally,

$\begin{matrix}{{NI} = {\frac{2}{\sqrt{2}}\sqrt{\left( {0.5 - {WWI}} \right)^{2} + \left( {0.5 - {OWI}} \right)^{2}}}} & (4)\end{matrix}$

The neutrality index (NI) refers to a quality control parameter thatdescribes the degree of deviation from neutrality and is given in therange [0,1]. An NI index of zero (0) validates the proppant sample'sneutrality, whereas an NI value of one (1) translates to a non-neutralwettability character even if the WI (wettability index value) was zero(0). FIG. 3 thus presents an interpretation of a range of outcomes onthe wettability index scale.

FIG. 4 illustrates example results of wettability parameters, inaccordance with one or more implementations. In particular, FIG. 4 showsthe computed wettability index for the exemplary proppant samples. Theimplementations disclosed herein thus address challenges of directmeasuring techniques for a proppant's wettability and the difficultiesin measuring the contact angle of spherical or irregular, small objects.

FIG. 5 illustrates an example visualization of a computed wettabilityindex of different hydrocarbons, in accordance with one or moreimplementations. In particular, FIG. 5 shows that the wettability ofproppant samples exhibit a relatively similar wettability status whentested with different hydrocarbon phases. Based on the wettabilityindex, the experimental results show that the overall wettability of theproppant samples can be characterized as neutral to slightly water-wet.Although the proppant samples' wettability index of zero (0) istypically a reflection of neutral wettability, this may not always betrue. For example, where water-wet and oil-wet indices are equivalentlyhigh (for example, WWI=OWI=0.8), WI is determined to be zero (0). Such acase indicates that the proppant phase has a strong but equal affinityto both aqueous and hydrocarbon phases. Thus, if WI results in a neutralcharacter, checking the degree of neutrality using equation (4) iswarranted Neutrality can thus be classified as follows:

-   -   NI is in the range [0, 0.1]: the sample is neutral.    -   NI is within the range [0.1, 0.3]: the sample is weakly neutral.    -   Else: wettability is non-neutral, with mixed wettability, or can        be termed “false neutral”.

FIG. 6 illustrates an example cap 600 of a three-dimensional(3D)-printed vessel 1200 for wettability assessment of fracturingproppants, in accordance with one or more implementations. The vessel1200 is illustrated and described in more detail with reference to FIG.12 . The vessel 1200 includes a base component 800 that has a threadedcylindrical portion 804. The base component 800 is illustrated anddescribed in more detail with reference to FIG. 8 . The cylindricalportion 804 of the base component 800 has a particular thread profile,and the base component 800 also defines a cavity 812 sized to contain aproppant sample. The cavity 812 is illustrated and described in moredetail with reference to FIG. 8 . The cap 600 is configured to bescrewed onto the threaded cylindrical portion 804 after the proppantsample is injected into the cavity 812. A surface of the cap 600 isshaped to flatten a proppant surface of the proppant sample. The cap 600is also threaded with the particular thread profile of the cylindricalportion 804.

FIG. 7 illustrates an example cap 600 of a 3D-printed vessel 1200 forwettability assessment of fracturing proppants, in accordance with oneor more implementations. The cap 600 is illustrated and described inmore detail with reference to FIG. 6 . The vessel 1200 is illustratedand described in more detail with reference to FIG. 12 . In someimplementations, the vessel 1200 (including the cap 600) is 3D printedusing at least one of engineering plastic, tough resin, or acrylonitrilebutadiene styrene (ABS). Engineering plastic refers to a group ofplastic materials that have better mechanical or thermal properties thanthe more widely used commodity plastics. Examples of engineering plasticinclude thermoplastic materials. Tough resin is a material that has thefeel and mechanical properties of ABS. Tough resin can withstand strainand high stress. For example, parts printed with tough resin can have atensile strength of 55.7 MPa and a 2.7 GPa modulus of elasticity. ABSrefers to a thermoplastic polymer having impact resistance andtoughness.

However, it will be noted that in other embodiments the vessel 1200and/or the cap 600 can be or include a metallic material, a non-metallicmaterial, or some combination thereof. For example, in some embodimentsthe vessel 1200 and/or the cap 600 can be or include a non-metallicmaterial that is based on a technique such as fused deposition modeling(FDM), stereolithography (SLA), selective laser sintering (SLS),material jetting (MJ), or some other non-metallic material or technique.Additionally or alternatively, the vessel 1200 and/or cap 600 can be orinclude a metallic material that is based on a technique such asselective laser melting (SLM). Some materials that can be used for thevessel 1200 and/or the cap 600 can be or include polylactide (PLA),carbon reinforced PLA, polyethylene terephthalate glycol (PETG), ABS,nylon 12 (PA12), tough resin, carbon reinforced resin, stainless steel316L, 718 nickel alloy, or some other similar or appropriate material.It will be understood that these listed techniques or materials areintended as examples herein, and other embodiments may include differenttechniques or materials for one or both of the vessel 1200 and the cap600.

In some implementations, the cap 600 is configured to apply pressure tothe proppant surface when the cap 600 is screwed onto the threadedcylindrical portion 804, such that the proppant surface is level. Thethreaded cylindrical portion 804 is illustrated and described in moredetail with reference to FIG. 8 . In some implementations, the cap 600is further configured to be tightened by a wrench after the cap 600 isscrewed onto the threaded cylindrical portion 804. In some embodiments,a wrench, hex key, or some other type of device is printed of the samematerial as the cap 600, and used to tighten or loosen the cap 600. Inthis embodiment, the use of the device to tighten or loosen the cap 600can help reduce or eliminate wear and tear on the cap 600.

FIG. 8 illustrates an example base component 800 of a 3D-printed vesselfor wettability assessment of fracturing proppants, in accordance withone or more implementations. In some implementations, the base component800 has a threaded cylindrical portion 804 extending outward from afirst side 808 of the base component 800. The cylindrical portion 804has a particular thread profile. For example, a screw mechanism having athread profile of #8-63 inch can be used, which results in a beneficialpitch to compress the proppant. Such a thread profile is also amenableto be manufactured using 3D printing. To flatten and level the proppantsurface by compaction, the cap 600 has the same thread profile. The cap600 is illustrated and described in more detail with reference to FIGS.6, 7 . The cap 600 is screwed onto the base component 800 afterinjecting the proppant into a cavity 812. The base component 800 definesa cavity 812 sized to contain a proppant sample. The cap 600 isconfigured to be screwed onto the threaded cylindrical portion 804 afterthe proppant sample is injected into the cavity 812. In someimplementations, the vessel 1200 (and thus base component 800) is 3Dprinted using at least one of engineering plastic, tough resin, or ABS.

FIG. 9 illustrates an example pin 900 of a 3D-printed vessel 1200 forwettability assessment of fracturing proppants, in accordance with oneor more implementations. The vessel 1200 is illustrated and described inmore detail with reference to FIG. 12 . The pin 900 is configured to bepartially screwed onto a second side 1104 of the base component 800before the proppant sample is injected into the cavity 812. The secondside 1104 is illustrated and described in more detail with reference toFIG. 11 . The cavity 812 is illustrated and described in more detailwith reference to FIG. 8 . The second side 1104 of the base component800 is opposite to the first side 808 of the base component 800. Thefirst side 808 of the base component 800 is illustrated and described inmore detail with reference to FIG. 8 .

In some implementations as shown in FIG. 9 , the pin 900 has a hexagonalopening sized to receive a screwdriver to screw the pin 900 onto thesecond side 1104 of the base component 800. For example, the pin 900 canbe designed with a 4.3 mm hexagonal opening for a screwdriver. Afterinjecting the proppant sample into the vessel 1200, the cap 600 istightened (for example, using a 14 mm wrench). While the proppant sampleis enclosed within the vessel 1200, the pin 900 is fully screwed inuntil it tightens. The cap 600 can then be opened, such that theproppant sample is ready for the test. In some implementations, thevessel 1200 (and thus pin 900) is 3D printed using at least one ofmaterials or techniques described above.

FIG. 10 illustrates an example pin 900 of a 3D-printed vessel 1200 forwettability assessment of fracturing proppants, in accordance with oneor more implementations. The vessel 1200 is illustrated and described inmore detail with reference to FIG. 12 . In some implementations, the pin900 is configured to be fully screwed onto a second side 1104 of thebase component 800 after the proppant sample is injected into the cavity812. The second side 1104 is illustrated and described in more detailwith reference to FIG. 11 . The base component 800 and cavity 812 areillustrated and described in more detail with reference to FIGS. 8, 11 .

FIG. 11 illustrates example components of a 3D-printed vessel 1200 forwettability assessment of fracturing proppants, in accordance with oneor more implementations. The vessel 1200 is illustrated and described inmore detail with reference to FIG. 12 . The vessel 1200 includes a basecomponent 800 having a threaded cylindrical portion 804 extendingoutward from a first side 808 of the base component 800. The threadedcylindrical portion 804 and first side 808 are illustrated and describedin more detail with reference to FIG. 8 . The cylindrical portion 804has a particular thread profile. The base component 800 defines a cavity812 sized to contain a proppant sample. The cavity 812 is illustratedand described in more detail with reference to FIG. 8 . A cap 600 isconfigured to be screwed onto the threaded cylindrical portion 804 afterthe proppant sample is injected into the cavity 812. A surface of thecap 600 is shaped to flatten a proppant surface of the proppant sample.The cap 600 is threaded with the same, particular thread profile. A pin900 is configured to be partially screwed onto a second side 1104 of thebase component 800 before the proppant sample is injected into thecavity 812. The second side 1104 is opposite to the first side 812.

FIG. 12 illustrates an example assembly of a 3D-printed vessel 1200 forwettability assessment of fracturing proppants, in accordance with oneor more implementations. In particular, FIG. 12 shows the cap 600screwed onto the threaded cylindrical portion 804 of the base component800. The cap 600 is illustrated and described in more detail withreference to FIG. 6 . The threaded cylindrical portion 804 and the basecomponent 800 are illustrated and described in more detail withreference to FIG. 8 . The cap 600 is threaded with the same, particularthread profile as the base component. Not visible in FIG. 12 is the pin900, which is screwed onto a second side 1104 of the base component 800.The second side 1104 is illustrated and described in more detail withreference to FIG. 11 .

In some implementations, the 3D-printed vessel 1200 is part of awettability measurement system. The wettability measurement system isdescribed in more detail with reference to FIGS. 1, 2A. The wettabilitymeasurement system includes a wettability measurement instrument and thevessel 1200. The wettability measurement instrument is also described inmore detail with reference to FIGS. 1, 2A. The wettability measurementinstrument includes a housing (sometimes referred to as a cell) and adropping needle attached to the housing. The dropping needle is to applya droplet of deionized water or a hydrocarbon to the proppant sample.The vessel 1200 is configured to be placed into the housing of thewettability measurement instrument, such that the vessel 1200 iscentered with respect to the dropping needle.

The vessel 1200 is used for wettability assessment of small sphericalobjects, for example, proppant samples. The vessel 1200 thus enablesnumerical wettability measurement of small spherical surfaces using apendant drop method. Wettability measurement is performed using thecontact angle technique. The proppant samples used are small sphericalobjects of material that is used in reservoir hydraulic fracturingprimarily to keep an induced fracture open. The wettability of theproppants thus plays an important role in increasing the flow back offracturing fluids and the recovery of produced hydrocarbons. Wettabilitymeasurement is needed for proppants to assess the degree of neutralityor their deviation from neutral wettability character (that is, oil orwater preferentiality).

The assembled vessel 1200 is designed to fit inside a built-in housingof a contact angle determination system (for example, the KRUSSDSA-100). However, the vessel 1200 as is, or with minor designmodification, can fit in various contact angle-measuring equipmentavailable in the market. The contact angle determination system issometimes referred to as a wettability measurement instrument. In someimplementations, the vessel 1200 has a diameter in a range from 2.5 cmto 3 cm, however in other embodiments the diameter of the vessel 1200can be larger or smaller. The diameter of the vessel 1200 can be basedon, for example, the equipment in which the vessel 1200 is intended tofit. Such a diameter size prevents the wall effect because the diameterof the vessel 1200 is three times the size of the droplet. In addition,the design and dimensions of the vessel 1200 can be modified to fitwithin other contact angle determination systems. A purpose of thevessel 1200 is to compact the proppant in a limited space. In someimplementations, a length of the vessel 1200 is in a range from 3 cm to4 cm. However, in other embodiments the length of the vessel 1200 can belarger or smaller. The length of the vessel 1200 can be based on, forexample, the equipment in which the vessel 1200 is intended to fit. Thelength of the vessel 1200 is important to ensuring the stability of theproppant while it is transferred and placed into the measuringinstrument. For example, an optimal example length is 3.5 cm. Theproppant capacity inside the vessel 1200 is designed to be relativelysmall to reduce the amount of material used in manufacturing and tooptimize the amount of proppant particles used in testing.

FIG. 13 illustrates an example computer system for wettabilityassessment of fracturing proppants, in accordance with one or moreimplementations. In the example implementation, the computer system is aspecial purpose computing device. The special-purpose computing deviceis hard-wired or includes digital electronic devices such as one or moreapplication-specific integrated circuits (ASICs) or field programmablegate arrays (FPGAs) that are persistently programmed to perform thetechniques herein, or can include one or more general purpose hardwareprocessors programmed to perform the techniques pursuant to programinstructions in firmware, memory, other storage, or a combination. Suchspecial-purpose computing devices can also combine custom hard-wiredlogic, ASICs, or FPGAs with custom programming to accomplish thetechniques. In various embodiments, the special-purpose computingdevices are desktop computer systems, portable computer systems,handheld devices, network devices or any other device that incorporateshard-wired and/or program logic to implement the techniques.

In an embodiment, the computer system includes a bus 1302 or othercommunication mechanism for communicating information, and one or morecomputer hardware processors 1308 coupled with the bus 1302 forprocessing information. The hardware processors 1308 are, for example,general-purpose microprocessors. The computer system also includes amain memory 1306, such as a random-access memory (RAM) or other dynamicstorage device, coupled to the bus 1302 for storing information andinstructions to be executed by processors 1308. In one implementation,the main memory 1306 is used for storing temporary variables or otherintermediate information during execution of instructions to be executedby the processors 1308. Such instructions, when stored in non-transitorystorage media accessible to the processors 1308, render the computersystem into a special-purpose machine that is customized to perform theoperations specified in the instructions.

In an embodiment, the computer system further includes a read onlymemory (ROM) 1310 or other static storage device coupled to the bus 1302for storing static information and instructions for the processors 1308.A storage device 1312, such as a magnetic disk, optical disk,solid-state drive, or three-dimensional cross point memory is providedand coupled to the bus 1302 for storing information and instructions.

In an embodiment, the computer system is coupled via the bus 1302 to adisplay 1324, such as a cathode ray tube (CRT), a liquid crystal display(LCD), plasma display, light emitting diode (LED) display, or an organiclight emitting diode (OLED) display for displaying information to acomputer user. An input device 1314, including alphanumeric and otherkeys, is coupled to bus 1302 for communicating information and commandselections to the processors 1308. Another type of user input device isa cursor controller 1316, such as a mouse, a trackball, a touch-enableddisplay, or cursor direction keys for communicating directioninformation and command selections to the processors 1308 and forcontrolling cursor movement on the display 1324. This input devicetypically has two degrees of freedom in two axes, a first axis (e.g.,x-axis) and a second axis (e.g., y-axis), that allows the device tospecify positions in a plane.

According to one embodiment, the techniques herein are performed by thecomputer system in response to the processors 1308 executing one or moresequences of one or more instructions contained in the main memory 1306.Such instructions are read into the main memory 1306 from anotherstorage medium, such as the storage device 1312. Execution of thesequences of instructions contained in the main memory 1306 causes theprocessors 1308 to perform the process steps described herein. Inalternative embodiments, hard-wired circuitry is used in place of or incombination with software instructions.

The term “storage media” as used herein refers to any non-transitorymedia that store data and/or instructions that cause a machine tooperate in a specific fashion. Such storage media includes non-volatilemedia and/or volatile media. Non-volatile media includes, for example,optical disks, magnetic disks, solid-state drives, or three-dimensionalcross point memory, such as the storage device 1312. Volatile mediaincludes dynamic memory, such as the main memory 1306. Common forms ofstorage media include, for example, a floppy disk, a flexible disk, harddisk, solid-state drive, magnetic tape, or any other magnetic datastorage medium, a CD-ROM, any other optical data storage medium, anyphysical medium with patterns of holes, a RAM, a PROM, and EPROM, aFLASH-EPROM, NV-RAM, or any other memory chip or cartridge.

Storage media is distinct from but can be used in conjunction withtransmission media. Transmission media participates in transferringinformation between storage media. For example, transmission mediaincludes coaxial cables, copper wire and fiber optics, including thewires that include the bus 1302. Transmission media can also take theform of acoustic or light waves, such as those generated duringradio-wave and infrared data communications.

In an embodiment, various forms of media are involved in carrying one ormore sequences of one or more instructions to the processors 1308 forexecution. For example, the instructions are initially carried on amagnetic disk or solid-state drive of a remote computer. The remotecomputer loads the instructions into its dynamic memory and send theinstructions over a telephone line using a modem. A modem local to thecomputer system receives the data on the telephone line and use aninfrared transmitter to convert the data to an infrared signal. Aninfrared detector receives the data carried in the infrared signal andappropriate circuitry places the data on the bus 1302. The bus 1302carries the data to the main memory 1306, from which processors 1308retrieves and executes the instructions. The instructions received bythe main memory 1306 can optionally be stored on the storage device 1312either before or after execution by processors 1308.

The computer system also includes a communication interface 1318 coupledto the bus 1302. The communication interface 1318 provides a two-waydata communication coupling to a network link 1320 that is connected toa local network 1322. For example, the communication interface 1318 isan integrated service digital network (ISDN) card, cable modem,satellite modem, or a modem to provide a data communication connectionto a corresponding type of telephone line. As another example, thecommunication interface 1318 is a local area network (LAN) card toprovide a data communication connection to a compatible LAN. In someimplementations, wireless links are also implemented. In any suchimplementation, the communication interface 1318 sends and receiveselectrical, electromagnetic, or optical signals that carry digital datastreams representing various types of information.

The network link 1320 typically provides data communication through oneor more networks to other data devices. For example, the network link1320 provides a connection through the local network 1322 to a hostcomputer 1324 or to a cloud data center or equipment operated by anInternet Service Provider (ISP) 1326. The ISP 1326 in turn provides datacommunication services through the world-wide packet data communicationnetwork now commonly referred to as the “Internet” 1328. The localnetwork 1322 and Internet 1328 both use electrical, electromagnetic oroptical signals that carry digital data streams. The signals through thevarious networks and the signals on the network link 1320 and throughthe communication interface 1318, which carry the digital data to andfrom the computer system, are example forms of transmission media.

The computer system sends messages and receives data, including programcode, through the network(s), the network link 1320, and thecommunication interface 1318. In an embodiment, the computer systemreceives code for processing. The received code is executed by theprocessors 1308 as it is received, and/or stored in storage device 1312,or other non-volatile storage for later execution.

FIG. 14 illustrates an example process for using a 3D-printed vessel forwettability assessment of fracturing proppants, in accordance with oneor more implementations. In some implementations, the processillustrated in FIG. 14 is performed by the wettability assessment systemillustrated and described in more detail with reference to FIGS. 11, 13.

The wettability assessment system screws (1404), partially, a pin 900 ofa 3D-printed vessel 1200 onto a base component 800 of the vessel 1200.The pin 900 is illustrated and described in more detail with referenceto FIGS. 9, 10 . The base component 800 is illustrated and described inmore detail with reference to FIG. 8 . The vessel 1200 is illustratedand described in more detail with reference to FIG. 12 . The basecomponent 800 has a first side 808 and a second side 1104 opposite tothe first side 808. The first side 808 is illustrated and described inmore detail with reference to FIG. 8 . The second side 1104 isillustrated and described in more detail with reference to FIG. 11 . Thepin 900 is screwed onto the second side 1104 of the base component 800.

The wettability assessment system injects (1408) a proppant sample intoa cavity 812 defined by the base component 800. The cavity 812 isillustrated and described in more detail with reference to FIG. 8 .

The wettability assessment system screws (1412) a cap 600 of the vessel1200 onto a threaded cylindrical portion 804 of the base component 800to flatten, by a surface of the cap 600, a proppant surface of theproppant sample. The cap 600 is illustrated and described in more detailwith reference to FIG. 6 . The threaded cylindrical portion 804 isillustrated and described in more detail with reference to FIG. 8 . Thethreaded cylindrical portion 804 extends outward from the first side 808of the base component 800. The cylindrical portion 804 and the cap 600have a particular thread profile. For example, a screw mechanism havinga thread profile of #8-63 inch can be used, which results in abeneficial pitch to compress the proppant. Such a thread profile is alsoamenable to be manufactured using 3D printing. To flatten and level theproppant surface by compaction, the cap 600 has the same thread profile.

The wettability assessment system tightens (1416), by a wrench (forexample, using a 14 mm wrench), the cap 600 onto the threadedcylindrical portion 804 of the base component 800. The cap 600 appliespressure to the proppant surface when the cap 600 is screwed onto thethreaded cylindrical portion 804 and then tightened, such that theproppant surface is leveled.

The wettability assessment system screws (1420), fully, the pin 900 ontothe base component 800 of the vessel 1200. In some implementations asshown in FIG. 9 , the pin 900 has a hexagonal opening sized to receive ascrewdriver to screw the pin 900 onto the second side 1104 of the basecomponent 800. For example, the pin 900 can be designed with a 4.3 mmhexagonal opening for a screwdriver. While the proppant sample isenclosed within the vessel 1200, the pin 900 is fully screwed in untilit tightens. The cap 600 can then be opened, such that the proppantsample is ready for the test.

The wettability assessment system unscrews (1424) the cap 600 to providea wettability assessment of the proppant sample. For example, the vessel1200 is placed into a wettability measurement instrument, such that thevessel 1200 is centered with respect to a dropping needle of thewettability measurement instrument. The dropping needle applies adroplet of deionized water or a hydrocarbon onto the proppant surface toprovide the wettability assessment. For example, the wettabilitymeasurement instrument captures an image of a droplet contacting theproppant sample. The wettability measurement instrument determines acontact angle of the droplet and the proppant sample based on the image.The wettability assessment is based on the contact angle.

FIG. 15 illustrates an example process for wettability assessment offracturing proppants, in accordance with one or more implementations. Insome implementations, the process illustrated in FIG. 14 is performed bythe wettability assessment system illustrated and described in moredetail with reference to FIGS. 1, 11, and 13 .

A wettability measurement system removes (1504) moisture from at leastone fluid line of the wettability measurement system using a solvent. Insome implementations, prior to measuring the contact angle, thewettability measurement system removes moisture from at least one fluidline of the wettability measurement system using a solvent. To preparethe system for contact angle measurement, the wettability measurementsystem is calibrated. The fluid lines are cleaned and dried. Forexample, solvents are used to ensure the absence of fluids inside thelines. This step is performed to prevent fluid remains (for example,leftover fluids from previous measurements) that can mix with thetesting phase, and alter its properties and affect the wettabilityresults.

The wettability measurement system injects (1508) a proppant sample intoa vessel 1200 of the wettability measurement system. The vessel 1200 isfurther illustrated and described with reference to FIG. 12 . In someimplementations, the vessel 1200 has a diameter less than a dimension ofthe wettability measurement instrument, described in more detail withreference to FIG. 1 . For example, the proppant sample is injected intoa transparent semi-cylindrical vessel having an outer diameter that isless than an inner dimension of the wettability measurement instrument.

A flat surface of the wettability measurement system applies (1512)pressure on a proppant surface of the proppant sample, such that theproppant surface is level. For example, the vessel 1200 is filled withthe proppant sample and a pressure is applied to the surface of theproppant sample by a flat surface. The flat surface can be a surface ofthe cap 600, illustrated and described in more detail with reference toFIG. 6 . The application of the pressure is repeated until the proppantsurface is optimally leveled. The proppant surface is leveled to reducethe effect of spaces between proppant particles.

The wettability measurement system places (1516) the vessel 1200 into awettability measurement instrument, such that the vessel 1200 iscentered with respect to a dropping needle of the wettabilitymeasurement system. The implementations disclosed herein enable andfacilitate numerical wettability measurement of small spherical surfaces(for example, having a mesh size of 5-80) using a pendant drop methodbased on the KRUSS drop shape analysis (DSA)-100. The wettabilitymeasurement system can include a wettability measurement instrument,such as the KRUSS DSA-100, an actuator (such as implemented in a roboticarm) to perform physical actions on the vessel 1200 and the wettabilitymeasurement instrument, and a computer system 1302 to control thewettability measurement instrument and the actuator. The computer system1302 is further illustrated and described with reference to FIG. 13 .

The dropping needle of the wettability measurement system applies (1520)a droplet of deionized water or a hydrocarbon onto the proppant surface.In some implementations, the proppant sample is positioned inside thewettability measurement instrument, such that the droplet contacts theproppant sample at a location greater than a threshold distance from awall of the vessel 1200. Thus, wall effect is reduced or eliminated. Thedroplet is prevented from touching or approaching the walls of thevessel 1200 using the disclosed implementations. When traditionalmethods are used, touching or being close to a vessel wall can cause thedroplet's adhesion to be dominated by the wettability of the vesselitself and not the proppant sample. For example, when water is appliedto a graduated cylinder, the fluid surface will be curved creating ameniscus caused by the fluid's attachment to the walls. Using theimplementations disclosed herein, the proppant sample is positionedaccurately below the dropping needle instead to mitigate wall effect. Insome implementations, the size of the vessel 1200 is increased, furtherdecreasing the wall effect, for example, in case a wall effect isobserved.

The wettability measurement system captures (1524) an image of thedroplet contacting the proppant sample to provide a wettabilityassessment of the proppant sample. In some implementations, the image ofthe droplet contacting the proppant sample is captured within athreshold time after the droplet is applied onto the proppant surface.For example, after the droplet is released, the image is frozen within athreshold time in a range of seven to twelve seconds. The threshold timeis designed to mitigate the effects of pore spaces between proppantparticles. In some implementations, the wettability measurement system(for example, the computer system 1302) determines the contact angle ofthe droplet and the proppant sample based on the image.

The computer system 1302 is further illustrated and described withreference to FIG. 13 . The wettability assessment is based on thecontact angle. For example, the contact angle of the proppant samplewith the droplet phase is computed using software on the computer system1302. The wettability assessment can include computing the indicesillustrated and described in more detail with reference to FIG. 5 .

FIG. 16 illustrates an example process for identifying a wettabilityindex of fracturing proppants, in accordance with some implementations.The technique may include determining, at 1604 for a proppant sample, afirst value related to an oil-wet index of the proppant sample. Thefirst value may be, for example, OWI as described above with respect toFIG. 3 .

The technique may further include determining, at 1608 for the proppantsample, a second value related to a water-wet index of the proppantsample. The second value may be, for example, WWI as described abovewith respect to FIG. 3 .

The technique may further include determining, at 1612 for the proppantsample based on the first value and the second value, a third valuerelated to a wettability index of the proppant sample. The third valuemay be, for example, WI as described above with respect to FIG. 3 .

The technique may further include determining, at 1616 based on thethird value, a wetting characteristic of the proppant sample. Aspreviously noted, the WI index values may range from −1, whichcharacterizes a strong oil wettability character (e.g., a wettabilitycharacteristic) to 1, indicating a strong water wettability character(e.g., another wettability characteristic).

In some embodiments, the technique may include performing a hydraulicfracturing procedure that includes the proppant based on the wettingcharacteristic of the proppant. For example, the wetting characteristicmay serve as the basis for selection of a particular proppant for ahydraulic fracturing procedure, the amount of proppant used, whether oneproppant is mixed with another, etc.

It will be understood that techniques such as those of FIGS. 14-16 areintended as example techniques, and may vary in other embodiments. Forexample, elements may be performed in an order differently thandepicted, concurrently with one another, etc. Some embodiments mayinclude more or fewer elements than depicted. Other variations may bepresent.

What is claimed is:
 1. A method comprising: injecting a proppant sampleinto a vessel wherein, the vessel compacts the proppant sample insidethe vessel; applying pressure on a proppant surface of the proppantsample by a flat surface to reduce spaces between particles of theproppant sample, such that the proppant surface is level; applying adroplet of deionized water or a hydrocarbon onto the level proppantsurface; and capturing an image of the droplet contacting the proppantsample to provide a wettability assessment of the proppant sample. 2.The method of claim 1, further comprising determining a contact angle ofthe droplet and the proppant sample based on the image, wherein thewettability assessment is based on the contact angle.
 3. The method ofclaim 1, further comprising heat aging the proppant sample to removemoisture from the proppant sample.
 4. The method of claim 1, wherein thedroplet is applied by a pendant drop method.
 5. The method of claim 1,wherein the proppant sample is positioned inside the vessel, such thatthe droplet contacts the proppant sample at a location greater than athreshold distance from a wall of the vessel.
 6. The method of claim 1,wherein the image of the droplet contacting the proppant sample iscaptured within a threshold time after the droplet is applied onto theproppant surface.
 7. The method of claim 1, wherein the vessel is level.